A. Field of the Invention
The present invention relates to spraying apparatus and more particularly to spraying apparatus for spraying suspensions or solutions from a fixed wing aircraft having predetermined characteristics independent of the speed of the aircraft carrying out the spraying.
B. Description of the Prior Art
Mosquito-borne diseases affect millions of people worldwide each year. In the United States, some species of mosquitoes can transmit diseases such as enciphalitis, dengue fever, and malaria to humans, and a variety of diseases to wildlife and domestic animals. To combat mosquitoes and the public health hazards they present, many states and localities have established mosquito control programs. These programs, which are based on surveillance, can include nonchemical forms of prevention and control as well as ground and aerial application of chemical and biological pesticides.
The first step in mosquito control is surveillance. Mosquito specialists conduct surveillance for diseases harbored by domestic and non-native birds, including sentinel chickens (used as virus transmission indicators), and mosquitoes. Surveillance for larval habitats is conducted by using maps and aerial photographs and by evaluating larval populations. Other techniques include various light traps, biting counts, and analysis of reports from the public. Mosquito control programs also put high priority on trying to prevent a large population of adult mosquitoes from developing so that additional controls may not be necessary. Since mosquitoes must have water to breed, methods of prevention may include controlling water levels in lakes, marshes, ditches, or other mosquito breeding sites, eliminating small breeding sites if possible, and stocking bodies of water with fish species that feed on larvae. Both chemical and biological measures may be employed to kill immature mosquitoes during larval stages. Larvicides target larvae in the breeding habitat before they can mature into adult mosquitoes and disperse. Larvicides include the bacterial insecticides Bacillus thuringiensis israelensis and Bacillus sphaericus, the insect growth inhibitor methoprene, and the organophosphate insecticide temephos. Mineral oils and other materials form a thin film on the surface of the water which cause larvae and pupae to drown. Liquid larvicide products are applied directly to water using backpack sprayers and truck or aircraft-mounted sprayers. Tablet, granular, and briquet formulations of larvicides are also applied by mosquito controllers to breeding areas.
Adult mosquito control may be undertaken to combat an outbreak of mosquito-borne disease or a very heavy nuisance infestation of mosquitoes in a community. Pesticides registered for this use are adulticides and are applied either by aircraft or on the ground employing truck-mounted sprayers. State and local agencies commonly use the organophosphate insecticides malathion and naled and the synthetic pyrethroid insecticides permethrin, and sumithrin for adult mosquito control.
Mosquito adulticides are applied as ultra-low volume (ULV) spray. ULV sprayers dispense very fine aerosol droplets that stay aloft and kill flying mosquitoes on contact. ULV applications involve small quantities of pesticide active ingredient in relation to the size of the area treated, typically less than 3 ounces per acre, which minimizes exposure and risks to people and the environment. Some communities have thermal foggers that use an oil carrier that is heated to disperse the pesticide in a dense smoke-like fog.
The best time to kill adult mosquitoes by fogging is at dusk, when they are most active and looking for food (mosquitoes feed on human or animal blood). The aerosol fog primarily targets flying mosquitoes, which is why the timing of the spray is critical.
The most commonly used products are synthetic pyrethroid insecticides (such as Scourge and Anvil), pyrethrins and malathion. All insecticides used for mosquito control must be registered with the U.S. Environmental Protection Agency (EPA). During the fogging, flying mosquitoes within the treated area are killed. Although the local mosquito population is reduced for a few days, fogging does not prevent mosquitoes from re-entering the area.
Currently, ultra-low volume (ULV) applications of adulticides represent one of the most widely used and effective methods for control of mosquitoes in urban and suburban areas. Experiments to determine the relationship between insecticidal droplet size and kill of adult mosquitoes were conducted using laboratory wind tunnel tests with monodisperse aerosols and field tests with ground ULV aerosol generators. Previous research has shown that the effectiveness of these applications is fundamentally related to the particle or droplet size of the aerosol. This is particularly true for applications which depend on direct contact of the insecticide with the insect body.
Latta et al. (1947) conducted a laboratory wind tunnel study with uniform droplet sizes of DDT which indicated that 12 to 20 μm diameter was optimum for adult mosquito control with wind velocities of 2 to 8 mph. La Mer et al. (1947) indicated that the optimum droplet size for mosquito control was 15.8 μm in a theoretical analysis. Mount et al. (1968) reported that malathion aerosols with 6 to 10 μm volume median diameter (VMD) were more effective with 11 to 22 μm VMD when applied with truck-mounted equipment in field tests with caged mosquitoes.